Saturday, August 18, 2012

In a Field of Goldenrod

Kids and naturalists wielding bug nets ventured into the tangled vegetation. Sweeping the nets from side to side among the grasses and flowers, these budding entomologists soon discovered the diversity of life hiding in an overgrown field.

Plumes of yellow goldenrod flowers danced in the breeze next to succulent stalks of common milkweed, and insects buzzed in the warm sunshine. While goldenrod flowers get a bad reputation for being the cause of summer allergies, their heavy pollen grains do not drift through the air and into our nostrils. The brilliant yellow heads composed of many tiny florets and the leafy green stalks provide food and shelter for a myriad of insects, and insects were what we were hoping to find.

My first catch, since I was one of the participating “kids” on this bug collecting expedition, was a beautiful grasshopper with red hind legs. Appropriately named the red-legged grasshopper, Melanoplus femurrubrum (from femur=thigh, rubrum=red), it is one of the most common grasshoppers in North America, with the center of its population directly over the Midwest.

Red-legged grasshoppers have good nutrition down pat, eating a variety of plant species in a single meal. Those fed on just one type of plant, even if it is the seemingly nutritious alfalfa, developed health issues and produced fewer eggs. The way they eat is interesting, too. The poet Mary Oliver observed a grasshopper “the one who is eating sugar out of my hand, who is moving her jaws back and forth instead of up and down,” and described it in her poem “The Summer Day.” It is from that poem that I learned that grasshoppers do indeed move their jaws back and forth to chew!

The chewing action of the goldenrod gall fly, Eurosta solidaginis, does more than just facilitate eating. After a female gall fly deposits an egg into the stem of a goldenrod plant, the egg hatches in about ten days, and the larva immediately starts eating the stem from the inside out. The chewing action and the larva’s saliva, which is thought to mimic plant hormones, cause the goldenrod’s stem to thicken into a dense, round gall.

Sliding my bug net over the top of a goldenrod flower, I caught a beautiful orange-belted bumblebee, Bombus ternarius. I was glad to have a closer look, because I’d seen several on prairie blazing star (pretty purple flowers) at the Forest Lodge Nature Trail recently, and wondered what they were. These smaller bees tend to forage at the tips of the goldenrod flower clusters, while letting bigger bees occupy the cluster’s center.

Looking closely at the center of a goldenrod flower cluster, I notice a deviation in the pattern of blossoms. As I peered closer, the smooth round body and eight legs of a goldenrod crap spider came into focus. This tiny hunting spider has a short, broad abdomen, and legs that are held outstretched to the side that enable it to move sideways, forward and back just like a crab.

Goldenrod flowers are a great spot for this spider to wait in ambush for bees, wasps, butterflies, moths and other nectar-seeking insects. To camouflage itself from the eyes of both predators and prey, crab spiders can change from the yellow to white, depending on the color of the flower they live on.

Some consider goldenrod a weed, while others plant it in their gardens. When sorting and identifying the diversity of insects trapped by our nets, it is evident that no matter what we think, many insects like goldenrod just fine.

And, just for the record, it is ragweed—not goldenrod—that makes you sneeze.

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